Differential ability of th1 and th2 cells to undergo activation-induced apoptosis and association with BCL-2 expression

We have examined the ability of a panel of human Thl and Th2-type cells to undergo activation-induced apoptosis. CD3receptor stimulation of Thl clones, in the absence of antigenpresenting cell (APC)-derived costimulation, resulted in apoptotic death of the cells. Addition of antibodies to the CD28 costimulatory molecule prevented apoptosis induction in the Thl clones. In contrast, the Th2 clones were resistant to apoptosis under the same stimulating conditions. The ability of the Th2 clones to resist apoptosis was not due to a lack of expression of either Fas or its ligand. However, the levels of Bcl-2 protein expression correlated with resistance to apoptosis. It was observed that the levels of expression of Bcl-2 protein was higher in the Th2 clones, whereas the Thl clones expressed only low levels. These data suggest that CD3-receptor occupancy may generate distinct downstream events in the two T cell subsets.